Windshield cleaning system



June 14, 1960 F. R. wEYMoUTH, .1R 2,940,109

WINDSHIELD CLEANING SYSTEM 2 Sheets-SheetI l Filed Oct. 29, 1956 4. L,nl..

IN VEN TOR. fff/m/z. wif/naam .111. BY @W MMY@ A r fm2/v5 ys June 14,1960 F1 R. wEYMoUTH, .1R 2,940,109

WINDSHIELD CLEANING SYSTEM 2 sheets-sheet' 2 Fild 001'.. 29, 1956 Fig 6ATTORNEYS United. States Patent 2,940,109 wnsDsHmLD CLEANING SYSTEMFrederick' R. Weymouth, Jr., Buffalo, N;Y., assignor to Trico ProductsCorporation, Butalo, N .Y.

Filed Oct. 29, 1956, Ser. No. 618,804

9 Claims. (Cl. 15--250.02)

` This invention relates to windshield cleaning systems and moreparticularly to a windshield cleaning system having an electricallyoperated wiper motor and a vacuum powered washer fluid pump, said motorand pump being coordinated for operation in a certain predesignatedmanner.

. It is becoming common practice in motor vehicles of current design toinstall windshield cleaner systems which contribute greatly toward safervehicle operation by eliminating the hazards associated with dirtywindshields. Many types of windshield washer systems have been devisedand are in current usage. The present invention is concerned with theapplication of a washer system to a motor vehicle employinganelectrically powered Wiper motor, and having a vacuum operated fluidpump, wherein the operation of the wiper motorand fluid pump iscoordinated to obtain automatic operation in a predesignated manner. Thepresent invention represents an improve-` ment in such types ofwindshield cleaner systems andiis characterized by a simplified controlmeans which provides reliable and effective coordinated washer and wiperoperation. The control means of the invention also provides for theindependent control of the wiper motor when it is desired to performwiping operation independently of washer operation. Y

The main object of this invention is to provide an improved windshieldwasher system for use on motor vehicles having an electrically poweredwiper motor and a vacuum powered washer iiuid pump.

v A further `object of this invention is to provide a control meanswhichprovides wiper motor operation independently of Washer pump operation.

Another object of. this invention is to provide a washerwiper systemwhich is reliable yand eiiicient in operation.

These and further objects and features of the invention will .becomemore apparent from the following description and the accompanyingdrawings wherein: v

Fig 1 is a fragmentary perspective View of a motor vehicle having awasher-wiper system embodying the principles of the invention;

Fig. 2 is an enlarged cross-sectional view of a control element used inthe system of the invention;

Fig. 3 is an enlarged cross-sectional view of a coordinating mechanismused with a washer uid pump included in the system of the invention;

Fig. 4 is a section view as seen from line 4 4 in Fig. 2;

Fig. 5 is an end view of the control element as shown in Fig. 2; and

. Fig. 6 is a schematic diagram illustrating the electrical circuit usedin the system of the invention.

Referring now to the drawings and more particularly to-'Fig 1, thenumeral 11 identities a motor vehicle naving awindshield 12 on which`are arranged a pair of wiper blades 13 movable over predesignated areasby wiper arms 14 Amounted for oscillating motion by means of anelectrically powered wiper motor 16, all in the usual manner. Awindshield cleaning system. arranged for the co-.

ordinated washing and wiping of the windshield, includes Patented June14, 1960 a reservoir assembly 17, having a pump unit 18 which is vacuumpowered to provide a predesignated quantity of cleaning fluid to beejected upon the windshield via hose or conduit 19, and jet means 21.

The pump unit 18 includes `a spring loaded piston 22 arranged formovement in one direction as a result of pressure differential caused bycompletion of a vacuum circuit to charge the pump with liquid, andmovement in the opposite direction by expansive action of a spring meanswhen the vacuum circuit is broken to discharge the liquid .in the pump.For further description of a vacuum operated pump of such type,reference is had to Patent No. 2,649,332, issued August 18, 1953.

A control assembly 23, forming the main part of the invention andadapted for the control of the wiper motor 16 and the coordinated4operation of the reservoir assembly 17, is arranged in the vehicle forconvenient manipulation by the vehicle operator.

The reservoir assembly includes a coordinator unit 24 mounted on `areservoir cover 26, which unit is adapted to coordinate the operation ofthe pump 18 and the wiper motor 16 to achieve a complete windshieldcleaning cycle. The coordinator unit 24, which is more fully describedin copending patent application Serial No. 530,970, filed August 29,1955, now Patent No. 2,877,486, comprises a top section 27, a bottomsection 28, and a top and bottom intermediate section 29 and 31respectively, said four sections being held together by suitablefastening means (not shown). v

A vacuum chamber 32, formed within the top section and top intermediatesection, is divided by a diaphragm 33 supporting a plunger 34 forlimited downward move-y ment. The vacuum chamber 32 is connected by apassageway 36 with a hose or conduit 37 leading to a vacuum source, suchas the engine intake manifold. A chamber 38, formed within the topintermediate section and the bottom intermediate section, contains adiaphragm-39 which is engaged by the end of the plunger 34 on thetopsurface, and by the end of a spacer 41 on the bottom surface. Thechamber 38V opens into an atmospheric chamber 42 providing a venting ofthe pump piston chamber to atmosphere via port means 43, clearancearound the spacer 41, and chamber 38. A valve 44, supported on thespacer 41, is arranged to engage a seat 46 to cut olf said venting ofthe pump piston chamber to atmosphere when the spacer is moveddownwardly. A compression spring 47, surrounding the spacer and engagingthe valve 44 at one end, maintains ,the end of the spacer in contactwith the bottom of the diaphragm 39. Supported on the Opposite end ofthe spacer is a normally closed valve 48 which covers a circular vacuumrecess 49 connected by a passageway 51, to the passageway 36, to thusprevent evacuation of the air -in the pump chamber above the piston 22.A vent 52, arranged in the plunger 34, provides for the equalization ofpressure on either side of the diaphragm 33. A nipple 53, which connectswith the vacuum chamber 32 above the diaphragh 33, is arranged forconnection with a hose or conduit 54 which leads to the control assembly23, and which is adapted for connection of the top portion of chamber 32to atmosphere for initiation of pump operation.

It will be seen that with vacuum condition existing on each side of thediaphragm 33.in the chamber 32, the various movable parts will be in theposition illustrated in Fig. 3, and the region above thepump piston 22will be connected with the atmosphere. However, admittance ofatmospheric pressure to the ltop portion of the chamber 32 via nipple53, will cause a pressure differential upon the plunger 34 and thediaphragm 33,

resulting in the downward movement of said plungery connection to thepump chamber above pump piston 22, and rconnecting the pump pistonchamber with a source of vacuum via the recess 49, passageways 51, 36,and the hose 37. As a result thereof, the `pump piston 22 will be forcedupwardly in the pump chamber and a given seating of the valve 48 `andthe unseating of the valve 44. Such action will result in the connectionof the upper partv of vthe pump piston chamber with Yatmosphere in themanner as above described. The upward movement of the pump piston`resulted in the 'compression of Ya spring 56, which `can nowk expandand rforce the piston downwardly, whereupon liquid will be eiected fromthe pump unit into a hose or 'conduit 57 and into a passage-A way58-formed in a nipple 59 yprovided in 'the lbottom section 28. Saidliquid 'flow will continue past a llap type check valve 61, and yinto apassageway v62 of a nipple 63 formed in the bottom intermediate section31, and then into the hose 19 for delivery to the surface of thewindshield. A portion of the liquid flow in the passageway 58 will be-diverted into apassageway 64 and will `ilow past a check valve `66,entering a hydro= static chamber 6'7 tobuild up hydrostatic pressureacting against the bottom of a diaphragm 68. The hydrostatic chamber 67is formed in the bottom intermediate section, while opposite and on the'other side of the diaphragm 68, is formed Van atmospheric chamber 69which is vented to atmosphere by 'a passageway 7'1. A vbleed ber 67drops suicientiy to allow a reseating of the valve 7'4 which will againconnect the "chamber 72 with at# for providing maintenance of vacuumcondition in the screw and passageway arrangement `(not shown) isVprovided for the controlled 'flow of liquid from the hydrostaticchamber 67 back into the passageway 64, thus providing a time controlfor .the release of hydrostatic pressure in the chamber 67.

f 4A chamber 72, formed in the top section Z7 and opposite lthe4'chamber 69, is lconnected by a passageway 73 to the vacuum passageway36, the -end of the passage- Way `73"-being normally lclosed by a valve74. Chamber 72 `is kvented tov atmosphere through a notch 76 formed inthe wall ofthe seat supporting the valve 74, and about the stern of avalve lifter 77 into the atmospheric chamber 69. The lower endfof thevalvevllifter 77 is arranged to vrest upon the diaphragm 68, while theopposite endis pointed fior entry into an elastic sleeve member 78.Compressively arranged between lthe elastic sleeve 78 Vand the valve 74is a helical Aspring 79 which normally keeps the -valve seated tightlyupon the open endof the passageway 73. The elastic sleeve '78 ispositioned in alignment with a passageway S1 formed in a nipple y82 towhich is aiiixed a hose or conduit 83 leading to and connected with anipple 84, lformed on the control assembly 23. The sleeve 78 acts as aValve against the pointed end 'of "the valve lifter 77 to seal oi airllow into the hose 83 during extreme pressure fluctuations which mightotherwise dissipate the vacuum in said hose. The sleeve being elasticand distensible, will readily permit air flow from the hose 83 but notin a reverse air flow.

It will be seen that in the normal, -or non-operative posi-tion of theparts above described, the valve 74 will be seated and atmosphericpressure Willexistin the chamber 69, chamber 72 and hose f8.3. As vthepump unit 18 is caused to operate lto discharge a given quantity ofliquid, hydrostatic pressure will be built up Vin the chamber 67 causingan upward ymovement of vthe valve lifter 77, compressing the spring '79to make connection ci the chamber 7?, with the rsource-oi? vacuum viapassageways 73 and 36. Upward lmovement of the valve lifter 77 willterminate when the enlarged -liead thereof engages the t'opsurface ofthe atmospheric chamber 69, thus cutting off connection of the chamberi72 lwith atmo'sphere. Vacuum conditions will thus "be maintained in the'hose `83 until the hydrostatic pressure `in the vchainhose 83, is toprolong operation :of thenwiper motor 16 after completion of liquidspray so that the wiper blades. will wipe the windshield dry.A'Suchmotor control action' is a function'of the control assembly 23,which will now be described.

The control assembly 23 includes a cylindrical front housing 86 and acylindrical rear housing 87 held together by fastening means such asscrews 88. Supported within the rear end vof the front housing is aplate 89 formed of an electrical insulating material on which areconcentrically arranged sliding electrical conducting contacts 91, 92,93, and variable resistance 94, as best 'seen in Fig. 6. A `pair ofresilient electrical conducting iingers 96 `and9l are arranged ou theplate 89, linger '96 being in permanent electrical lconnection with theend of the sliding contact 93, While ringer 97 is in permanent elec#trical connection'with the end of sliding Contact 92. The

free end of resilient linger 96 is arranged for 'movableV electricalcontact with the end ofthe resistance 94,while` the free end of theresilient `linger 97 is arranged 'for movable electrical contact withthe end `of sliding contact 91. Supported in the front housing 86 foraxial and rotatable movement, Yis "a lshaftf98 the inner endiof whichhas secured thereto an electrical insulating plate. 99, the outer'end'of which has aiiixed thereupon a con-j trol vknob 101 adapted for `therotary adjustment of 'the' shaft 98. A pair of electrical conductinglingers 102 'and 103 are pivotally attached to `the plate 99, finger 102being varranged for sliding engagement with the contacts 91 and 92,while finger ,103 Yis arranged for sliding engagement with contact 93and variable resistance '94. A helical spring104, surrounding the shaft98, is 'compressively arranged between Ythe inside `oi the fronthousing86 and the plate y99 to Aurge the `lingers i102 and.' 103 in slidableengagement with the contacts 91,9193,

and variable resistance 94. i

` On the back surface of the rear Ihousing v87 `is'formed av vacuumchamber 106 in which is Aslidably arranged a piston 107 having a lpistonshaft 108 that extends forwardly through the plate 89 `forengagementwith Cthe end of the shaft 98. A heIicalspring 109, positionedin 'the vacuum chamber 106, surrounds the shaft 108 and Viscompressively arranged between the end of the .vacuum chamber and theside of the piston 107 to urge the latter rearwardly in the vacuumchamber.

The pistonV shaft 108 supports an electrical non-conducting plate 111arranged for engagement with the free ends of the fingers 96 and `97.The rear end of the vacuum chamber y106 4is opento atmosphere yby means0f holes 11,2, to provide a pressure differential upon the piston 107when vacuum pressure is provided in "the vacuum chamber v106 on theinner side of the piston 107. It will be seen that 'such a pressuredifferential will cause movement of the piston 107 resulting in theaxialshifting of the shaft 98 by reason -of engagement of shaft 108, thusmoving the electrical lingers i102 and 103 out of engagement withcontacts 91, 92, 93, and variable resistance 94, and causing the plate111 to f orce thefingers 96 and 97 into engagement withl the end of resistance 94 and contact 91 respectively. Y

lPositioned for axial Amovement Ywithin-tl-teknob 101is a button 113,the inner end of which is arranged rfor l abutment with a rod 114rotatably supported within tire rod 114v is maintained Ain abutmentwitha -cap 117 ai?-V fixed tothe end of a stem 118 supporting vat valve119 normally arranged in abutment upon a seat 121. The valve 119 ismaintained in seated engagement by means of a helical spring 122 whichis compressively arranged between the valve 119 and a nipple fitting 123towhich 1hosel 54 is attached It will be seen that when the button 113is depressed, the rod 114 will move the cap- 117 and stem 118 axially tounseat the valve 119 and allow air flow under atmospheric pressure topass vfrom the holes 112 into the hose 54.

The control assembly 23 may be adapted for use with an electric motorhaving an electrical circuitfsuch, for example, las illustrated in Fig.6. The motor 16 has an amature winding 126, and a field winding 127 incircuit with the variable resistance 94. The armature circuit includes asolenoid 128, which when activated, causes closing of contacts 129. Aparking linkage arrangement, as generally illustrated by numeral 131, isadapted for opening the circuit in the field winding after thewipermotor has moved the wiper blades .13 to parked position to shut offthe motor. It will be seen that when the control knob 101 is rotated tocause the conducting finger 103 to establish a circuit between thecontact 93 and the end of the variable resistance 94, the conductingfinger 102 will -be caused to establish electrical circuit between thecontacts 91 and 92, current will iiow from a battery 132, through thearmature winding 126, solenoid 128, contact 92, finger 102, contact 91to ground. The solenoid 128, being energized, will draw the lever 132 toclose electrical contacts 129 `thereby continuing electrical circuitfrom the armature winding 126, across the armature brushes 133 toground, and also through the field winding 127, contact 93, conductingfinger 103, part of the variable resistance 94, lto contact 92, throughconducting tinger 102, and contact 91,V to ground, thus energizing thewiper motor. As the control k-nob 101 is rotated, a greater proportionof the variable resistance 94 will be added to the field windingcircuit, resulting in increasing the speed of wiper -motor operationuntil a maximum, or full on position, is realized. The use of thecontrol knob 101 is intended for the sole operation of the wiper motor.vWhen it is desired to perform a windshield wiping and washingoperation, it is only necessary to depress the button 113. Such actionwill initiate a complete washer and wiping operation as follows:

Axial movement of the rod 114, as a result of depression of button 113,will unseat the valve 119 allowing flow of air under atmosphericpressure into the hose 54 and into the vacuum chamber 32 on the top sideof the diaphragm 33. The resulting pressure differential acting upon thediaphragm 33 will cause downward movement of the plunger 34 and resultin the pumping of a given A quantity of cleaning liquid, which will besprayed upon the windshield, in the manner as has been set forth indetail heretofore. During the spraying of liquid upon the windshield,hydrostatic pressure will be built up in the chamber 67 to unseat thevalve 74 and connect the hose 83 to a source of vacuum in the manner asalso above described. Vacuum condition will thus be established in thevacuum chamber 106A of the control assembly, resulting in a pressuredifferential upon the piston 107 and the movement of the latter to causeelectrical contacts of the fingers 96 and 97, and disruption of theelectrical contact of the fingers 102 and 103. In such position of themovable elements of the control assembly, electrical circuit will becompleted from the battery through the armature winding 126,solenoid'128, contact l92, iinger 97, contact 91, to ground.Energization of solenoid 128 will move the lever 132 to engage thecontacts 129 to complete the circuit from the armature winding 126,across the armature brushes 133 to ground, and also through the fieldwinding 127, contact 93, finger 96, through the `full length of thevariable resistance 94, to the contact 92, finger 97, and contact 91 toground.

Mare

As a result, the wiper motor will be operated at high speed during theremainder of the liquid spraying operation, and for a'period aftercessation of the liquid sprayingoperation. Wiper motor operation will becontinued while the hydrostatic pressure in the chamber 67 is graduallyreduced by the liquid bleeding process, which in due coursel will resultin the seating of the valve 74 and the connection of the chamber 72 withatmosphere to provideV ow of air, under atmospheric pressure, in thehose 83, as heretofore described. Flow of atmospheric pressure from hose83 into the control assembly chamber.106, will result in theequalization of pressure on each side of the piston 107, whereupon thespring 109 will move the piston rearwardly to non-operative position,following which the electrical circuit contacts in the control assemblywill be returned to their pre-interrupted condition.

It is to be noted that if the wiper motor was not being operated when awindshield washer and wiping cycle was initiated, the motor will bereturned to non-operative position upon completion of such cycle; and ifthe wiper motorhad been operating at some speed, dependent upon theadjustment of the control `knob 101, prior to initiation of a washingand wiping cycle, the motor will automatically be returned to continueoperation at the said speed.

From t-he lforegoing it will be seen that the stated objectives of theinvention can. be realized in a reliable and etiicient manner byapplication of the principles of the invention as set forth in detailhereinabove.

The foregoing description has been'given in detail without thought oflimitation since the inventive principles involved are capable ofassuming other physical embodiments without departing from the spirit ofthe invention and the scope of the appended claims.

' What is claimed is: y

1. A windshield cleaning system comprising in combination anelectrically powered wiper motor, a reservoir assembly having a pressureuid responsive pump unit operable to discharge a given quantity ofcleaning iiuid for use upon the windshield, a coordinator unit operableto provide operation of the pump unit and concurrently therewithoperation of the wiper motor and to maintain operation of the wipermotor after cessation of pump unit operation, and a common controlassembly arranged to initiate the independent operation of the wipermotor and to initiate operation of the coordinator unit to in turninitiate concurrent operation of the pump unit and the wiper motor.

2. A vehicle windshield cleaning system comprising in combination anelectrically powered wiper motor, a reservoir assembly having a vacuumpowered pump unit operable to discharge a given quantity ofy cleaninguid for use upon the windshield, a coordinator unit mounted upon thereservoir assembly and operable to provide operation of the pump unitand concurrently therewith operation of the wiper motor and to maintainoperation of the wiper motor after cessation of pump. operation, and acommon control assembly positioned for convenient use by the Vehicleoperator, said control assembly having `means for the independentoperation of the wiper motor and further means to initiate operation ofthe coordinator unit to in turn initiate concurrent operation ofthe pumpunit and the wiper motor.

3. A vehicle windshield cleaning system comprising in combination anelectrically powered wiper motor, a reservoir assembly having a pumpunit responsive rto a pressure differential to charge the pump unit witha given quantity of cleaning liquid and having a resilient meansactionable after termination of said pressure differential to eject saidcleaning Iliquid for use upon the windshield,I a coordinator unitmounted upon t-he reservoir assembly and operable to initiate operationof the pump unit and of the wiper motor concurrently therewith, and acommon control assembly positioned for convenient use by the ve-4.A1vel1icle winds-hield cleaning system comprising .in

combination :anelectrically powered Wiper motor, a rescrvoiriassemblyhavinga pump unit responsive to .a :pressuie ldiierentialtofcharge thepump with .a given quantity yof cleaning liquid and having resilientmeans .actionable after .termination :ofsaid pressure differential .toejectssaid' cleaning liquid-,for use upon the windshield, a #pressurefluid responsive coordinator unit mounted upon the reservoir assemblyand operable tjo initiate concurrent operationot the 'pump unit and "thewiper motor and `:tocontinue operation of the 'Wiper-.motor for apredetermined time a=fter cessation of pump operation, and acentrolassembly positioned 1forconvenient-useby the vehicle operator, saidcontrol assembly having electrical circuit vmeans to initiate operationofy the wiper motor independendyof the pump unit and having pressureduid control means v'arranged-tocause operation of the coordinator unit.v f

-In a vehicle `Windshield cleaning `system. including an electricallypowered wiper `motor and Va reservoir `'assembly having a Vacuumoperated pump unit adapted for the discharge of a given quantity -ofoleaning'liquicl for spraying 1predesignated"areas 'of thewindshield acontrol assembly arranged for `4convenient manual use by the vehicleoperatorrand'liavng first electrical circuit means for controllingyoperation *ofv the Wiper Ymotor findepend. ently of' 'said pump unitandpressure fluid responsive means `connectable Withl said reservoirassembly, ysaid piessure"'iiiid responsive means being adapted 'for thedisruption 'of said first electrical circuit means controllingindependent operation of the Wiper motor and being 'further adapted for'the establishment of second electrical circuit fmeans .providing wipermotor operation concurV rent with the operation of the pump unit.

'6. in a vehicle 4windshield cleaning system including an 'electricallypowered wiper mot-or and a reservoir assem-bly having a Vvacuum operatedpump unit adaptedfor the rdischarge of algiven quantity of cleaningliquid `forspraying'pre'designated'areas of the windshield', a controlassembly arranged for convenientv manual use `by the vehicle operator,Asaid control assembly having rotatable' "rneans including an electricalcircuit means adaptedto provide variabile speed motor operation, andhaving means to initiate operation of said pump unit andL-furt-her meansincluding a uid pressure Vdiierential arrangement conncctable with saidreservoir assembly and adapted `for the. disruption of said electricalcircuit meansand'for the Aestablishment of electrical circuits to:provide high yspeed Wiper motor operation during operation o'f saidpumpfunit and 'for a predesignated time thereafter.v f

l7. In *ave'hicle Windshield cleaning system including 'an electricallypowered Wiper motor and a reservoir assemblyhaving a vacuum operatedpump unit 'adapted orfthe discharge of a given lquantity of .cleaning'liquid for spraying predesignated areas of the Windshield, a

,control 'assembly arranged vfor convenient 'manual use'bythevehicleoperator, said lcontrol assembly fliaving va rotatable andaxially Amovable shaft, a plate containing electrica-1 circuit elements;means aflixed to the shaft Aincludingfe'l'ectrical circuit completingmembers positionabile for 'providing variable. speed .motor operation,axially movable means to initiate pump unit operation, piston meansresponsive to pressure Huid diierentialan'd having an axially 'movableshaft engageable with said rst .mentioned .shaft-.for disruption .of:the electricalcirplaced .from the .contact elements.

cuits providing variable speed motor operation, and a plate meansaffixed to the second mentioned axially mov.Y ableshaftjand adapted uponpiston movement to establish;

electrical circuits vvproviding high speed wiper motor operatiom-saidpiston v:means arranged Ifor oper-ation during pump unitoperation andfora tpredesignated time there-- atten. f ..1 1, Y.

.8; A control assembly comprising a pair of lcylindricalhousingmembersrsecured together to enclose an electrical,v insulating platemember, electric contact elements secured to 'the .plate member, one ofsaid elements providing a variable .resistance connectable in fticldwinding circuit of a motor, .a shaft supported-for rotatable and `axialmovement in therst of said housing members, a knob for rotation of saidshathe .second .ofsaid motor .housings beingormcd to provid-e a pistonchamber, a shaft aliixed to .thetpiston and proiecting through theplate-memher for engagement with-therirstmentionedshaft, an axiallymovable button supported lin ythe lmo'b, lrod means .projecting vaxiallythrough said shafts :one Iend arranged in abutment with-said button theother end arranged in abutment with a valve means .movable to admit flowof air under atmosphericgpressure tthroughsaid piston chamer cin-oneside .of lthe piston, .means to connect the opposite side of the pistonchamber with a source of vacuum, electrical conducting yelementsarranged lfor slidaole engagement with Ithe contact elements and beingsupported for rotary motion by saidrst mentioned shaft, and `fingersmounted :upon'saidgplate-mcmber and arranged `for establisbment ofelectrical vcircuits through the contact elements when said electricalconducting -eiernents are dis- 9. Av control, assembly comprising vfirstand second cylindrical housing .means affixed together to enclose an.

electrical insulatingjplate member, electr-ical conducting.contacts-arranged concentrically upon one iside `of the plate member,one .of said contacts forming a variable resistance .formater speedregulation, shaft means supported in ythe iirst housing member forrotary and ,axial movement and yhaving atiixed to the inner end thereofan electrical insulating plate supporting` a Apair of electricalconducting fingers, resilient means adapted to bear against said ngersupporting v.plate to ymaintain said yfingers .in slidable engagementwithsaid conducting contacts to regulate electric current .iiow .through.the control assembly, a -control knob mounted on the outer end of theshafty for relative Aaxial .movement therewith, .a button .operativelysupported by .the knob lfor zaxial movement, :a piston chamber formedfini-,the `housing member opposite -to that from which the shaftprojects, piston :means slidably arranged in :the chamber .andhavingashaft adapted.for axial-enfV gagement with saidfirst ymentioned shaft,a valve means being normally seatedrto prevent .iiovv lofair underatmospheric :pressure through the back end of :said chamber, arodmovableby said l button to. .unseat said valve means Ato allow flow'.of air .under atmospheric 4pressure .through the back end .of saidchamber, .a .resilient means adapted `to urgethepiston ,toward thebackend of thechamber, and an electrical .insulating plate .atixedltothe piston shaft forengagementxyith.iinger means affixed to .the -rst`.mentioned plate member-to complete an Velectrical .circuit throughvthe .conducting contacts .and .the full .length .of the .variable.resistance .when the pair .of electrical conducting .fingers are .movedout .of .engagement with the electrical conductingcontacts. n 4

References Cited. in 'the'iile ,o'f this-patent' yUran-3o .sr-ArasPATENTS 42,743,473 .onreint YiMay v1,119.56 FOREIGN PATENTS l'17.3.5,380 (instaurare tm sept?, 195,5.

